Field
The present application relates to an optical source, in particular, the present application relates to an optical source applicable to a coherent optical transceiver.
Related Background Art
A Japanese Patent Application laid open No. 2009-146992A has disclosed an optical module that installs a wavelength tunable laser diode (hereafter denoted as t-LD) for emitting continuous wave (CW) light and an optical modulator that modulates the CW light emitted from the t-LD. A feature of the optical module is that the optical modulator and the t-LD are disposed side by side within a housing, and optically coupled with an inner fiber.
Another Japanese Patent Application laid open No. 2004-327173A has disclosed an electrical connector of a surface mountable type. The electrical connector disclosed therein is mounted on the circuit board such that a receptacle thereof exposes an opening upward to receive a plug vertically inserted thereto. Thus, the electrical connector realizes the arrangement of the double-decker circuit board.
One type of optical transceivers has been known as the coherent transceiver that installs an optical module having both of a t-LD and an optical modulator. The t-LD emits a CW light with a preset wavelength and the optical modulator modulates this CW light. The optical module directly outputs the CW light as the local source used in a receiver unit of the optical transceiver, and indirectly outputs, through the optical modulator, the modulated light as a transmitting signal in a transmitter unit of the optical transceiver. In such an optical module, a wavelength of the CW light currently output from the t-LD is necessary to be precisely detected, and matched with a designed wavelength. The optical module is necessary, when the optical modulator has the arrangement of the Mach-Zehnder (MZ) type made of semiconductor material, to control a phase difference between two optical beams entering the MZ modulator, and to set optical power output from the optical modulator in a designed level. Thus, the optical modulator is inevitable to provide a circuit, in addition to a driving circuit that processes modulation signals entering the optical modulator, to control such various parameters in a DC and/or a low frequency (LF) mode. Moreover, such control circuits are requested to communicate with or to be commanded from the host system installed within the optical transceiver, or provided outside of the optical transceiver.
Meanwhile, an eager and continuous request to make an optical module in compact and to save power consumption becomes further strengthened. The optical module installing the t-LD and the optical modulator, in spite of intricate controls thereof and resultant expanded circuit sizes, is necessary to be formed in compact and simple. One solution is to use a specific electrical connector, which is often called as a stack connector. The stack connector, which has the arrangement of the surface mountable type, may stack two or more printed circuit board (PCB) without other components, such as flexible printed circuit boards (PCBs). However, as the number of the control parameters for the optical module increases, which means that the stack connector extracting the control signals from the optical module provides a number of pins, a precise arrangement of the stack connector on the circuit board becomes necessary.